Crystal structure of (acetonitrile-N)copper(I) cyanide, [Cu(CH3CN)][CN]

Abstract

C 3 H 3 CuN 2 , monoclinic, P12 1 /c1 (no. 14), a = 8.399(2) Å, b = 8.144(2) Å, c = 7.836(2) Å, b = 116.56(3)°, V = 479.4 Å 3 , Z = 4, R gt(F) = 0.024, wRref(F 2 ) = 0.059, T = 120 K. Source of materialCopper(I) cyanide (0.2 g) prepared according [1] and acetonitrile (HPLC-grade, 1 mL) were mixed together. This mixture was filled in a glass ampule (Duran, interior diameter 10 mm, length 80 mm) which was evacuated and sealed. Following annealing was performed in an electric resistance oven at a temperature of 423 K. After three weeks the ampule was taken out, rapidly cooled down to room temperature and the solids were separated from the solvent. By this procedure the title compound can by obtained as single phase. DiscussionHibble et al. have described the rather complex structural chemistry of CuCN, AgCN and AuCN [2]. They were able to refine C and N occupancies of CuCN. The results indicate a ¢head-to-tail¢ disorder of the cyanide groups. We tried to crystallize CuCN with ordered cyanide groups by solvothermal syntheses with acetonitrile as solvent. Single crystal X-ray structure analysis of the title compound in combination with X-ray powder phase analysis of the bulk material shows that only a solvate of copper(I) cyanide and acetonitrile could be obtained as single phase by the described synthesis. The refinement with the occupancies of C and N indicates ordered cyanide groups. Two of the three cyanide groups in the coordination sphere of copper are carbon linked to the copper atom, the third one is linked via the nitrogen atom.[Cu(CH 3CN)][CN] could be described as a two-dimensional network (Schläfli symbol 8 2 ·4; for Cu and C) of condensed (CuCN)4 rings perpendicular to [100]. The layers are undulated. Additionally, the copper atom is coordinated by the nitrogen atom of the acetonitrile molecule along [100]. A part of a single layer of the two-dimensional network is shown in the top of the figure, the interlocking of this layers by the acetonitrile molecules at the bottom. Plane [3,4] and undulated layers [5,6] of (CuCN) 6 rings or (CuCN) 8 rings [7] are already known. Layers built of (CuCN)4 rings are less common [8].

Structure and Bonding in Copper(I) Carbonyl and Cyanide Complexes

“…In cyano-bridged compounds, such as CuCN itself, a single Cu–C/N band is invariably observed, representing the average energy of the Cu–C and Cu–N bonds. The CN stretching frequency in CuCN complexes correlates well with the crystallographically determined Cu–C/N distance. − A decrease of about 35 cm –1 in ν CN corresponds to an elongation of about 0.1 Å. Solid-state spectra of CuCN should not be collected as KBr pellets, due to a reversible reaction between CuCN and Br – in the solid state. Like CO ligands, CN groups might be expected to show IR frequencies corresponding to weaker stretching when bridging.…”

“…Upon addition of ligands to the copper(I) centers in the CuCN chain, bands A–C show a decrease in frequency. Band D becomes nondegenerate, splitting into a higher and lower frequency pair of features …”